The present invention relates to an interface circuit for providing a translated single-ended output signal level responsive to an applied differential input signal of a different level and, more particularly, to a circuit for interfacing to differential compensated silicon sensors while providing a translated single-ended output level signal that is independent of zero pressure common mode output signal level of the sensor.
Temperature compensated differential pressure sensors are well knwon in the art for measuring the difference between pressures applied simultaneously to opposite sides of a diaphragm of the sensor to produce a differential output voltage at respective outputs. Such a pressure sensor is the MPX2000 family of pressure sensors manufactured by Motorola, Inc. In general such sensors provide a given output voltage over a range of several tens of millivolts as the pressure applied thereto is increased from zero to the full scale pressure range of the sensor. Further, all known differential pressure sensors produce a common mode output voltage at zero applied pressure.
In many applications the full scale output voltage range of the aforedescribed pressure sensors may be too small to be utilized without translating this voltage to a higher level. Instrumentation amplifiers have been used in the past to interface with these type sensors in order to provide a translated output signal. Although instrumentation amplifiers fulfill some needs, they also suffer from problems that need to be addressed. Typically, instrumentation amplifiers require both positive and negative power supplies wherein many applications require only the use of a single power supply. In addition, in many microprocessor applications, an interface circuit must be able to translate the differential sensor output voltage level to the required microprocessor input voltage level while providing a known voltage offset to the input of the microprocessor at zero differential pressure. Instrumentation amplifiers in general can not provide a zero pressure offset voltage offset which is independent of the common mode offset voltage of the sensor.
Thus, a need exists for a single power supply interface circuit for use with available differential pressure sensors which can provide a zero pressure output voltage that is independent of the sensor common mode offset voltage.